<form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post">
<p>
<?php
if (IsSet($postID)){
    ?><input type="hidden" name="post" value="<?php echo $postID;?>" />
<?php
}
?>
<textarea name="<?php echo $formtype;?>" id="comment" rows="5" cols="10"></textarea>
</p>
<p><input type="submit" name="submit" value="Submit" /></p>
</form>
